Welding device and welding torch

ABSTRACT

A welding device includes a welding station with a welding torch which is connected thereto and from which there extends a welding electrode with a free end. The welding electrode is electrically connected to a suitable electric welding power supply. After a fixation device provided for this purpose is released, the welding electrode is axially movable in the welding torch, so that the electrode can be adjusted in accordance with use. The welding electrode is accessible at an end remote from the free end to a drive member which is intended for and able to enter into co-action with the welding electrode in order to drive the welding electrode out of the welding torch.

The present invention relates to a welding device comprising a weldingstation with a welding torch which is connected thereto and from whichthere extends a welding electrode with a free end which, at least duringoperation, is electrically connected to an electric welding power supplyand which, at least after fixation means provided for this purpose arereleased, is received for axial movement in the welding torch.

Welding has become an indispensable technique for connectingparticularly metal parts to each other by fusion. A much-used formthereof is so-called fusion welding, wherein parts are mutuallyconnected by fusing the material in the vicinity of the weld seamwithout any pressure at all being exerted. An important fusion weldingmethod is so-called arc welding, wherein an electric arc is used to fusethe edges of the weld seam together with optionally added material,which may come for instance from the welding electrode. In the lattercase this is referred to as arc welding with a consumable metalelectrode. In arc welding a distinction can be made between open arcwelding, arc welding under a protective atmosphere and covered arcwelding under a powder cover. In arc welding under a protectiveatmosphere reactions with the outside air are prevented by surroundingthe molten pool with an inert shielding gas, in particular a noble gassuch as helium or argon. In addition to all types of iron and steel,rapidly oxidizing metals such as magnesium and aluminium can also bewelded under such a noble gas shield. Known forms of these weldingmethods are TIG (tungsten inert gas) welding, wherein a non-consumabletungsten electrode is usually applied, and MIG (metal inert gas)welding, wherein a consumable metal electrode is normally used. Thesupplied gas (mixture) is used here solely with a view to the abovestated protection of the workpiece against oxidation. In so-called MAG(metal active gas) welding the supplied gas plays a more active part inthat it also contributes to the conversion of energy around the weldseam.

Welding is still frequently carried out as manual work and hereinrequires a high degree of skill in order to achieve a high weldingquality. Particularly the reproducibility of the obtained welding resultis of great importance here. With a view to cost-reduction and processcontrol, however, recourse is increasingly being made where possible tomore automated forms of welding. Robotized welding in particular hashere become very common, especially in the automobile and aircraftindustry, and has spread to other branches of industry. Because awelding robot can be fully programmed and can position the welding torchrelative to the workpiece with a high degree of precision, a very highwelding quality can thus be achieved with an equally high degree ofreproducibility which is unrealistic in manual welding. A problem doeshowever occur in welding techniques where use is made of a consumablewelding electrode. Because this electrode becomes shorter during use,the distance from the tip of the electrode to the workpiece graduallybecomes longer when positioning relative to the workpiece is the same,which has immediate consequences for the arc and the welding result. Forthis reason many robotized welding techniques are limited to the use ofa non-consumable welding electrode, with the result that some metals canthus not be welded, or complicated calibration techniques are appliedtherein which greatly increase the cost price.

The present invention has for its object, among others, to provide awelding device and welding torch of the type stated in the preamble,with which the length of the welding electrode can be adjustedrelatively easily and automatically, so that this length can also beheld constant in the case of a consumable electrode.

In order to achieve the intended object, a welding device of the typestated in the preamble has the feature according to the invention thatthe welding electrode is accessible at an opposite end to a drive memberwhich is intended for and able to enter into co-action with the weldingelectrode in order to drive the welding electrode out of the weldingtorch. Because the welding electrode is herein accessible to the drivemember, which can be operated on command or automatically, the weldingelectrode can if necessary be continuously adjusted during operation.Particularly a decrease in the length of the welding electrode, as isinevitable in a welding process on the basis of a consumable weldingelectrode, can thus be compensated, whereby the welding process canproceed in fully automatic manner, even when such a consumable weldingelectrode is used.

The welding torch can in principle be embodied in different ways, takinginto account the desired accessibility of the welding electrode to thedrive member. In a particular embodiment however, the welding deviceaccording to the invention has the feature that the welding torchcomprises an outer casing with an opening which provides access to acavity into which the welding electrode protrudes with the opposite end,and that the cavity and opening are adapted to receive the drive membertherein on a side remote from the welding electrode. The location andsize of the opening are herein geared to the position of the weldingelectrode and the size of the drive member, so that a satisfactorymutual alignment can thus be obtained.

A further embodiment of the welding device has the feature according tothe invention that the fixation means comprise a clamping sleeve whichengages round the welding electrode and is directly accessible fromoutside. In order to enable a fully automatic adjustment thereof, thewelding device has the feature in a further embodiment according to theinvention that the clamping sleeve is provided with a forced control.The fixation of the welding electrode in the welding torch can thus bereleased or applied fully automatically by operating the forced control.A particular embodiment of the welding device according to the inventionhas in this respect the feature that the control comprises a gear rackon an outer end of a drive rod which engages on a toothing arrangedexternally on the clamping sleeve. The drive rod herein extends forinstance from a controllable pressure cylinder, the stroke of which isadjusted to the desired degree of unlocking and locking of the weldingelectrode in the clamping sleeve.

In a preferred embodiment the welding device according to the inventionis characterized in that the welding torch is provided with a resettingdevice which is able and intended to place the welding electrode at afixed distance outside the torch. A fixed length of the weldingelectrode outside the torch can be maintained relatively easily by theresetting device, which is particularly important in the use of aconsumable welding electrode. Ipso facto the distance from the outer endof the welding torch to the workpiece is hereby controllable, whichmakes a not inconsiderable contribution toward a sound welding result.

In respect of the resetting device, use can be made of electronicsensors, for instance optical sensors or pressure sensors, in order todetermine the length of the welding electrode outside the welding torch.A relatively simple but no less effective embodiment thereof is appliedin a further particular embodiment of the welding device according tothe invention with the feature that the resetting device comprises ayoke which is connected movably to the frame and provided with a stopwhich can be moved at the fixed distance under the torch. Duringoperation the stop and the welding torch are positioned relative to eachother to then drive the welding electrode out of the welding torch ontothe stop. After the fixation means have once again been applied and thestop removed, the welding torch is thus ready for use again with thedesired length of the free outer end of the welding electrode.

A further particular embodiment of the welding device has the featureaccording to the invention that the welding torch can be manipulatedfrom a base station to a workpiece and that the base station comprisesthe drive member and the resetting device. By here accommodating thedrive member and the resetting device in the base station, the weldingtorch can remain relatively compact so as not to adversely affect accessto positions on the workpiece which are more difficult to reach.

A further particular embodiment of the welding device has the featureaccording to the invention that the welding torch is arranged instationary manner in a frame which also comprises the drive member andthe resetting device. The frame herein provides for an efficientrelative alignment of the welding torch with the welding electrode onthe one hand and the drive member and the resetting device on the other.

In order to also allow processing of rapidly oxidizing metals, such asfor instance aluminium and magnesium, a further particular embodiment ofthe welding device according to the invention has the feature that thewelding torch is provided with supply means for supplying a protectiveshielding gas around a free outer end of the welding electrode. Duringoperation the workpiece will thus be surrounded at the position of theweld seam by a protective atmosphere of the shielding gas, for instancea noble gas such as helium or argon or carbon dioxide, and the ambientair at this position will be displaced. Owing to the oxygen-free, or atleast low-oxygen environment which is thus applied, oxidation on thesurface of the weld seam can be efficiently prevented. A furtherparticular embodiment of the welding device according to the inventionhas in this respect the feature that the welding electrode comprises aconsumable metal stick, in particular a consumable tungsten stick, withwhich an aluminium workpiece can thus be welded in satisfactory manner.

The invention also relates to a welding torch as applied in the abovespecified welding device according to the invention, and will now befurther elucidated on the basis of an exemplary embodiment and anaccompanying drawing. In the drawing:

FIG. 1 shows a perspective view of a welding torch of an exemplaryembodiment of a welding device according to the invention.

The welding device of FIG. 1 comprises a stationary welding torch 10which is accommodated in a frame 1 and in addition a conventionalwelding station, assumed to be sufficiently well known to a skilledperson and therefore not further shown, in which an electrical weldingpower supply for the welding torch and a gas cylinder or other containerwith a protective shielding gas are housed. Two electrical connectingcables extend from the welding station. A first of these is fixedlyconnected to an electrical connection of welding torch 10, while asecond bears a mass clamp and is clamped therewith at a suitable,electrically conducting location to the workpiece. In order to protectthe workpiece against oxidation at the position of the weld seam, acontinuous flow of a suitable, inert shielding gas can be conducted overthe workpiece during operation. Applied here as the shielding gas is anoble gas such as argon or helium, but other non-reactive or lessreactive gases such as carbon dioxide are also suitable for thispurpose. The gas is supplied from the container provided for thispurpose in the welding station via a conduit connected to a connection 2of the welding torch provided for this purpose. The shielding gas flowsvia this connection 2 and a hollow casing 11 of the welding torch to anopen outer end 12 where a free end 14 of a welding electrode 12 extendsoutside casing 11. The free, active end 14 of welding electrode 13 isthus continuously surrounded by shielding gas during operation, so thatambient air is displaced at this location. Welding torch 10 furthercomprises an inlet and outlet 3,4 for coolant conduits, so that theoperating temperature of the torch can be maintained at an acceptablelevel during operation.

In this embodiment use is made of a consumable tungsten electrode forwelding electrode 13 in order to hereby enable welding of an aluminiumworkpiece under a protective atmosphere of the noble gas applied.Welding electrode 13 is received for axial movement in torch 10, but isfixed therein during operation by means of fixation means provided forthe purpose. The fixation means here comprise a clamping sleeve 15 whichis directly accessible from outside and which engages round and fixedlyclamps the welding electrode 13. Electrode 13 can be released and lockedby rotating clamping sleeve 15 counter-clockwise and clockwiserespectively. In this embodiment use is made of a fully forcedadjustment. For this purpose clamping sleeve 15 externally comprises atoothing 16 in which a gear rack 17 engages which is arranged on an endof a piston rod 18 of a pressure cylinder (not further shown). Byextending the pressure cylinder the clamping sleeve 15 will rotateclockwise and thus clamp the electrode 13 fixedly in the torch, whileconversely, with operation of the pressure cylinder in the oppositedirection, the clamping sleeve 15 is loosened and the electrode 13 inthe torch is released.

The longer the welding torch is used, the shorter the consumable weldingelectrode 13 will become, whereby the arc has to bridge a greaterdistance to the workpiece. This latter will eventually work to thedetriment of a desired welding result. In order to avoid this, thewelding torch is equipped with an automatic electrode adjustment.According to the invention the welding electrode 13 is accessible forthis purpose to a drive member 20 on a side remote from the free end 14.Drive member 20 comprises a stop on an outer end of a piston rod 21 of apressure cylinder 22 which is mounted together with torch 10 in frame 1.By successively releasing clamping sleeve 15 and extending pressurecylinder 22 the welding electrode 13 will be driven out of the torch andonce again assume the desired length outside torch 10, whereafter theclamping sleeve can be tightened again.

So as to ensure that electrode 13 is always driven to the same, fixedlength outside torch 10, the welding torch is provided with a resettingdevice. The resetting device here comprises a yoke 30 connected movably,i.e. pivotally, to frame 1. On its outer end the yoke 30 comprises astop 31 for receiving the free end 14 of the welding electrode thereon.Yoke 30 is controlled fully automatically with a pressure cylinder 32coupled thereto. By extending a piston rod 33 hereof, the yoke 30 pivotsabout its pivot axis in the frame and the stop moves to a fixed distanceunder the frame. The welding electrode is then driven out of torch 10 inthe above stated manner until electrode 13 strikes with the free end 14bumps against stop 31. The welding electrode now once again has thedesired length outside torch 10 and can be fixed in the welding torchagain, whereafter the stop is removed by retracting pressure cylinder33. The welding torch is then ready for a subsequent operating cycle.

The above described adjustment of the welding electrode in the torchthus proceeds fully automatically and can be carried out as often as isnecessary to maintain the desired welding result.

Although the invention has been further elucidated above with referenceto only a single exemplary embodiment, it will be apparent that theinvention is by no means limited thereto. On the contrary, many othervariations and embodiments are possible ed within the scope of theinvention for a person with ordinary skill in the art. Instead of acalibrated setting making use of a resetting device in any form, use canthus also be made of a continuous adjustment of the welding electrodewhich takes into account a normal burn-off rate. Nor is the inventiononly suitable for a welding torch in stationary arrangement, but it isalso suitable for a mobile welding torch. An automatic adjustment of thewelding electrode can herein be integrated into the welding torch, butis advantageously disposed outside of it in order to keep the weldingtorch as compact as possible. In this case use is preferably made of awelding torch which can be manipulated using a separate base station inwhich the drive member and optionally a resetting device areaccommodated.

The invention is also suitable for a wide range of welding processes,varying in accordance with the material of the electrode and theoptionally used shielding gas. These welding processes are not limitedhere to those based on a consumable electrode, but can also make use ofnon-consumable electrodes. In addition to aluminium and other rapidlyoxidizing metals such as for instance magnesium, normal metals can alsobe welded using the device according to the invention. The inventionthus provides a very widely applicable device with which a weldingprocess can be carried out fully automatically.

1-12. (canceled)
 13. A welding device comprising: a welding station witha welding torch which is connected thereto and from which there extendsa welding electrode with a free end which, at least during operation, iselectrically connected to an electric welding power supply and which, atleast after fixation means provided for this purpose are released, isreceived for axial movement in the welding torch, wherein the weldingelectrode is accessible at an opposite end to a drive member which isintended for and able to enter into co-action with the weldingelectrode, and the drive member is provided with means to drive thewelding electrode automatically out of the welding torch.
 14. Thewelding device as claimed in claim 13, wherein the fixation meanscomprise a clamping sleeve which engages round the welding electrode andis directly accessible from outside, and that the clamping sleeve isprovided with a forced control.
 15. The welding device as claimed inclaim 14, wherein the control comprises a gear rack on an outer end of adrive rod which engages on a toothing arranged externally on theclamping sleeve.
 16. The welding device as claimed in claim 13, whereinthe welding torch is provided with a resetting device which is able andintended to place the welding electrode at a fixed distance outside thetorch.
 17. The welding device as claimed in claim 16, wherein theresetting device comprises a yoke which is connected movably to theframe and provided with a stop which can be moved at the fixed distanceunder the torch.
 18. The welding device as claimed in claim 16, whereinthe welding torch can be manipulated from a base station to a workpieceand that the base station comprises the drive member and the resettingdevice.
 19. The welding device as claimed in claim 16, wherein thewelding torch is arranged in stationary manner in a frame which alsocomprises the drive member and the resetting device.
 20. The weldingdevice as claimed in claim 13, wherein the welding torch is providedwith supply means for supplying a protective shielding gas around a freeouter end of the welding electrode.
 21. The welding device as claimed inclaim 20, wherein the welding electrode comprises a consumable metalstick.
 22. The welding device as claimed in claim 21, wherein the metalstick is a tungsten stick.